Many different procedures and products exist to control pests in export or import fruits before shipment or when received in the port of destination, with the purpose of avoiding the transmission of pests from a country to another.
Among the procedures traditionally used for this purpose, it can be mentioned the fumigation with methyl bromide, thermal treatments or storage to low temperature during long periods of time.
The treatment with methyl bromide, although quick and efficient, has a series of disadvantages. The product damages the ozone layer, the fumigation has to be carried out at high temperature, over 15° C., which implies to heat up the fruit which diminishes shelf life of fruit after the treatment, the gas is phytotoxic and therefore, it damages the fruit; the fruit treated with methyl bromide changes its flavor. Also, the methyl bromide, being very soluble in fatty tissues, it is easily absorbed by the operators and causes irreversible damages when being exposed even to non lethal concentrations.
The thermal treatments can be applied to some pests, but they always bear a great damage to the fruit and therefore, a drastic reduction of the shelf life of treated fruit, because it is not possible to assure that the whole fruit warms exactly to the desire temperature.
The cold storage, although does not damage the fruit in massive form, involves a high cost, since the fruit must be stored during periods of time that overcome 40 days with all the costs that implies to maintain the cooling system working, depreciation of facilities and equipments, and with the possible lost of value that implies the fact of not taking the fruit out on time.
In summary, given the characteristics of each treatment, the most viable treatment so far, has been the treatment with methyl bromide. However, as the gas is harmful for the ozone layer, many countries signed the Montreal Protocol, according to which they should try to eliminate or reduce to a maximum extent, the use of methyl bromide. All efforts are focused to find alternative to this gas.
For that reason, and for several years now, phosphine has been investigated as an alternative for the treatment of fresh fruit and vegetables.
Studies developed in Australia, New Zealand and USA for the control of pests in fresh fruit, have shown good results as for mortality of insects. However, they have had no good results in reference to quality of treated fruit, which had always suffered a damage.
This damage has been produced by two causes mainly: presence of ammonia and relatively high fumigation temperature, over 15° C., to which the tests have been carried out.
Only few years ago, until Horn Diluphos System, an equipment to dilute pure phosphine with air was invented, it had not been possible to apply pure phosphine for fumigations, since phosphine presents self ignition properties, at concentrations over 18000 ppm. Therefore, until that moment, the only possible way to apply phosphine, was through a reaction of hydrolysis of metal phosphides, which always generates ammonia and which is phytotoxic and thus damaging the fruit. Also, the metal phosphides practically do not react at low temperature, which eliminates the possibility to apply these products at low temperatures; also, the time required to generate phosphine gas can be also of several days, depending on the temperature and moisture.
The hydrolysis reaction requires a temperature higher than 15° C. to generate phosphine. Therefore, all the tests with phosphine for fruit fumigation were always carried out at high temperature, which damaged the fruit and reduced their shelf life.
Besides, it was of public knowledge that phosphine needed high temperatures to be able to eliminate the pests.
All previous tests were carried out at temperatures over 15° C. and therefore these tests proved to damage the fruit, a reason to consider phosphine as a non viable alternative for methyl bromide.
The publication in Spain ES 2093646, member of EP 0508984 family of patents (COMONWEALTH SCIENTIFIC INDUSTRIAL AND RESEARCH ORGANISATION) discloses a method and a device to fumigate with phosphine, an area that contains grain or a similar particulated material that consists in establishing a flow of constant lineal velocity through the grain, of a carrier gas containing phosphine, being the phosphine concentration in the carrier gas constant and between 4 and 200 micrograms per liter of gas, and having the carrier gas a flow velocity such that the gas separates from the surface of the grain or of a similar particulated material, at a speed between 0.5×10−4 and 2.0×10−4 meters per second.
The application CL1010-1996 that claims the priority UK 9511495.5 (DEGESCH DE CHILE LTDA.) discloses a process to generate a phosphine mixture and dilution gas, in which a metallic phosphide gets in contacts with liquid water in a generation space, hydrolyzing the metallic phosphide and liberating phosphine, which is extracted and diluted with a gas up to non flammable concentrations. This process is remarked because the metallic phosphide is liberated in the liquid water in the form of loose particles, free of phosphide powder, retarding agents of the hydrolysis and hydrophobic substances, and with the particularity that the generation space has an atmosphere of inert gas to the phosphine that is part, at least, of the dilution gas. On the other hand, the equipment used to carry out the process mentioned previously, is also disclosed.
The application CL 1011-1996 (DEGESCH DE CHILE LTDA.) discloses a metal phosphide composition for the phosphine production by means of hydrolysis, where the metallic phosphide is in the shape of particles of free fluency, and exempt of powder of metallic phosphide, hydrolysis retarding agents, specially coatings of hydrophobic substances and hydrophobic preservatives. Also the use of this composition to produce gas that contains phosphine and the process to prepare this composition is disclosed.
In the patent EP 0826307 the fumigation of stored particulated material is disclosed. Specifically, the device to carry out the simultaneous fumigation of any number of silos using a simple source of a mixture of carrier gas and a fumigant gas like phosphine is disclosed.